<template>
	<ul class="list">
		<li 
		class="item" 
		v-for="item of letters" 
		:key="item"
		:ref="item"
		@click="handleLetterClick"
		@touchstart="handleTouchStart"
		@touchmove="handleTouchMove"
		@touchend="handleTouchEnd"
		>{{item}}</li>
		
	</ul>
</template>

<script>
	export default{
		name:'CityAlphabet',
		props:{
			cities:Object
		},
		computed:{
			letters(){
				const letters = []
				for (let i in this.cities){
					letters.push(i)
				}
				return letters
			}
		},
		data () {
			return{
				touchStatus: false,
				startY:0,
				timer:null
			}
		},
		updated () {
			this.startY = this.$refs['A'][0].offsetTop
		},
		methods:{
			handleLetterClick(e){
				this.$emit('change',e.target.innerText)
			},
			handleTouchStart(){
				this.touchStatus = true
			},
			handleTouchMove(e){
				if(this.touchStatus){
					if (this.timer){
						clearTimeout(this.timer)
					}
					this.timer =setTimeout(() =>{
						const touchY =e.touches[0].clientY -79
						const index = Math.floor((touchY - this.startY)/20)
						if(index>=0 && index<this.letters.length){
							this.$emit('change', this.letters[index])
						}
					},16)
				}
			},
			handleTouchEnd(){
				this.touchStatus = false
			}
		}
	}
</script>

<style lang="stylus" scoped>
	@import '~styles/varibles.styl'
	.list
		display:flex
		flex-direction:column
		justify-content: center
		position:absolute
		top:1.5rem
		right:0
		bottom:0
		width:.4rem
		.item
			line-height:.44rem
			text-align:center
			color:$bgcolor

</style>
